The present invention relates to vehicle suspension systems and in particular to improvements in and relating to suspension systems for the rear wheels of a motor vehicle.
In xe2x80x98Hxe2x80x99 frame or xe2x80x98torsion beamxe2x80x99 rear suspension systems a pair of trailing arms are pivotally connected at their forward ends to the vehicle and carry means for rotatably attaching the wheels of the vehicle at their rear end. The trailing arms are interconnected intermediate of their forward and trailing ends by a transverse torsion member. Helical compression springs act on the trailing arms adjacent their trailing ends.
The torsion member of such suspension systems allows the trailing arms to move generally laterally together while permitting a degree of independent vertical movement of the wheels. However, due to lateral flexibility of the xe2x80x98Hxe2x80x99 frame, the lateral deformation induces undesirable dynamic steering effects. In order to overcome such effects, it has been proposed, for example in WO97/127373 and DE2424649, to pivot the trailing arms about bushes which are not parallel but are oppositely inclined to a transverse axis of the vehicle. In this manner, lateral forces acting on the bushes compensate for lateral distortion of the xe2x80x98Hxe2x80x99 frame.
The present invention relates to modifications to xe2x80x98Hxe2x80x99 frame suspension systems which negates the problem of lateral deformation of the xe2x80x98Hxe2x80x99 frame and permits adaption of the system to promote geometrically controlled passive steering effects as well as improved camber control.
According to one aspect of the present invention, a vehicle suspension system comprises first and second trailing arms, each trailing arm being mounted to the vehicle adjacent its forward end for pivotal movement about a transverse axis of the vehicle, a first trailing arm being located adjacent one side of the vehicle and adapted adjacent its trailing end to support a first wheel of the vehicle, a second trailing arm located adjacent the other side of the vehicle and adapted adjacent its trailing end to support a second wheel of the vehicle, the first and second wheels being located on a transverse axis of the vehicle, means being provided to control lateral separation of the trailing arms, and a pair of dynamic beams being secured at their forward and rearward ends longitudinally of the vehicle, one dynamic beam being located in juxtaposed relationship with each of the trailing arms, each trailing arm being connected adjacent its trailing end to the adjacent dynamic beams, at a point intermediate of the ends of the dynamic beam; wherein the forward ends of the trailing arms are pivotally attached to the vehicle by means of bushes with longitudinal compliance, minimal vertical compliance and controlled lateral compliance, while the dynamic beams are secured to the vehicle at their rearward ends with longitudinal compliance but with zero or minimal lateral compliance and at their forward ends with longitudinal compliance and with controlled lateral compliance.
In accordance with the present invention, the dynamic beams will permit resilient vertical movement of the trailing arms, while inhibiting lateral deformation and the adversely dynamic steering effects associated therewith. The dynamic beams will also strengthen the xe2x80x98Hxe2x80x99 frame of the suspension system giving improved fatigue life. When a lateral load is applied to the suspension system, for example when the vehicle is cornering, the forward end of the trailing arm/dynamic beam assembly will move laterally in controlled manner, while the rearward ends of the dynamic beams will remain fixed laterally, so that passive steering of the suspension will be controlled geometrically. In accordance with the preferred embodiment of the invention, the forward ends of the dynamic beams may be secured to the vehicle via the bushes which secure the forward ends of the trailing arms.
Lateral separation of the trailing arms may be controlled by means of a torsion member which extends laterally between the trailing arms, intermediate of the forward and trailing ends of the arms, in the manner of a conventional xe2x80x98Hxe2x80x99 frame suspension. However, according to a further preferred embodiment of the invention, laterally extending camber control arms are secured to the trailing arms intermediate of their forward and trailing ends, the camber control arms extending towards one another, the inner ends of the camber control arms being pivotally attached to the vehicle. In this manner, as the trailing arms move upward and downward, the camber control arms will cause the trailing arms to twist thereby altering the camber angle of the wheel supported thereby. The variation in camber angle achieved in this manner may be controlled by suitable positioning of the effective pivoting point of the camber control arms longitudinally relative to the trailing arms and the length of the camber control arms.
Moreover, camber control corresponding to the passive steering may be achieved by arranging for the pivot axis of the camber control arms to move laterally of the vehicle along a path inclined to a transverse axis of the vehicle. This may be achieved by the use of inclined links to pivotally connect the inner ends of the camber control arms to the vehicle body or by locating the camber control arm pivots in transversely inclined slots or grooves or inclined compliant bushes.
A toe control bar may furthermore be provided to interconnect the trailing arms laterally adjacent their forward ends, to control lateral separation of the arms. Alternatively, or in addition, a torsion bar may be used for this purpose and to control roll of the vehicle.
Any suitable design of bush which will provide the required compliance in respect of movement in the longitudinal, vertical and transverse directions, may be used in the present invention. However, void bushes which will provide compliance longitudinally with minimal vertical compliance and which are designed to provide controlled lateral compliance, when required, are particularly suitable.
The invention is now described, by way of example only, with reference to the accompanying drawings, in which: